The present invention relates to a thermoplastic elastomer composition excellent in oil resistance. More particularly, it relates to an oil-resistant thermoplastic elastomer composition which comprises a dynamically crosslinked mixture of an ethylene copolymer rubber comprising ethylene and an acrylate or methacrylate ester and an olefin polymer at a specific ratio, or a dynamically crosslinked mixture of an ethylene copolymer rubber comprising ethylene and an acrylate or methacrylate ester, an olefin polymer and an olefin copolymer rubber comprising ethylene and .alpha.-olefin at a specific ratio.
Thermoplastic elastomers, which are hereinafter referred to as "TPEs", have been developed for various fields such as automobile parts, electric appliance parts and mechanical parts because of their characteristics that valcanizing step is not required in comparison with valcanized rubbers and they can be processed by ordinary molding machine for thermoplastic resins. Among them, olefin TPEs are known, for example, in Japanese Patent Kokai No. 48-26838, as being superior in balance of price and properties. Thus, their use has been developed.
Recently, however, with rapid progress of technique in various industries such as of automobile, electric appliance and machinery, the olefin TPE has been required to have various properties for various parts. Especially, due to less oil resistance from valcanized rubbers, the olefin TPE became unsatisfactory for a wide range of application.
In order to improve oil resistance, attempts have been made to increase crosslinking degree of olefin copolymer rubber in olefin TPE by increasing content of olefin polymer or adding inorganic filler.
However, even if oil resistance can be improved by decreasing content of olefin copolymer rubber or increasing crosslinking degree of the olefin copolymer rubber, this, in turn, causes reduction of flexibility, deterioration of compressive permanent set and decrease of flowability upon processing and thus it was difficult to obtain a TPE composition superior in balance of properties.